Method of making electromagnetic transducers



April 6, 1954 F. G. BUHRENDORF I 2,674,031

METHOD OF MAKING ELECTROMAGNETIC TRANSDUCERS I Filed Dec. 5, 1952 2 Sheets-Sheet l F/GJ 4 INVENTOP By E a. BUHRENDORF A from Ev April 6', 1954 F. e. BUHRENDORF METHOD OF MAKING ELECTROMAGNETIC TRANSDUCERS 2 Sheets-Sheet 2 Filed Dec. 5, 1952 FIG. 5

INVENTOP F. 6. BUHRENDORF By V A TTORNEV Patented Apr. 6, 1954 METHOD OF MAKING ELECTROMAGNETIC TRANSDUCER-S Frederick G. Buhrendorf, We'stfield, N. J., assignor .to Bell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Original application November 2, 1951, Serial No.

254,537. Divided an her 5, 1952, Serial-No d this application Decemv 324,388

2 Claims. (Cl. 29155.57)

This invention relates to electromagnetic transducerheads. and more particularly to the method of making transducer heads of the kind shown and d'escribed in my copending application SerialNo. 254,537, filed November 2, 1951, of which the present application is a division.

The above-identified parent application discloses a high frequency recording-reproducing head of stable design themagnetic core of which is fixedly positioned prior to the formation of the pole tips by means of a glazed ceramic coating applied to the head assembly.

In accordance with the general features of this invention a magnetic core comprising one or more laminations of high permeability magnetic material, such as permalloy, is wound around a ceramic wafer triangularly shaped at one end and notched at two opposite sides. A coil, space wound on a ceramic form, is disposed adjacent each of said notched sides. The magnetic core is threaded through each of said coils and disposed between the triangular sides of said ceramic wafer and a low resistance metallic shield to form two pole tips. The entire assembly is coated with a ceramic material and fired to form a glazed coating. The pointed end of the wafer is then ground and lapped until the desired separation of the pole tips is obtained.

The coating of the magnetic head with a ceramic glaze provides a rigidly clamped pole tip assembly held permanently in adjustment once properly lapped.

The nature of the invention and its distinguishing features and advantages will be more clearly understood from the following detailed description and the accompanying drawings in which:

Fig. 1 is a view in front elevation of the assembled magnetic head;

Fig. 2 is a sectional view taken on the line 22 of Fig. 1;

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1;

Fig. 4 is a view in perspective partially eX- panded to show the structural features of the head components;

Fig. 5 is a sectional view taken on the line 5-5 of Fig. 1; and

Fig. 6 is a view in front elevation showing the actual dimensions of the magnetic head.

Referring now to the embodiment of the present invention shown in the accompanying drawings, 2 is a ceramic wafer triangularly shaped at one end and notched at two opposite sides.

The ceramic forms 4, about which the recording and reproducing coils B are wound, are mounted adjacent the notched sides of the wafer 2 and are held in position by means of the notched portions 8 and the magnetic core l0 which is wound around the wafer 2 and threaded through each of the forms 4 and the coils 6. The ends of the magnetic core ID are disposed between the triangular sides of the wafer 2 and a low resistance, non-magnetic shield l2 which is heldin position adjacent the wafer 2 by means of the ceramic pin Hi.

The shield I2 may be made of a material such as copper. The core Ill, which may be in the form of a ribbon having a thickness of 0.001 inch, is made of magnetic material, such as permalloy. The surface of the ribbon is coated with a layer of suitable inert insulating material, such as alundum in order to prevent metal contact between the core 10 and the shield l2 or the terminal wires I t. The terminal wires IS, the coils 6 and the wires I8 which connect the coils t in series are preferably of tungsten. The termina1 wires l6 and the connecting wires [8 are welded to the coils 5. The triangularlyshaped wafer 2 and the forms 4 may be made of a material such as steatite.

As shown in Fig. 4, the ceramic forms 4 comprise a male portion 20 and a female portion 22 which, when joined and held together by the coil 6, support the wires 16 and I3.

After the magnetic head is assembled, as shown in Fig. 1, it is coated with a ceramic material and fired. The ceramic coating should be so selected that the firing temperature of the coating coincides with the heat treating temperature of the magnetic core so that the glazing will be completed simultaneously with the heat treatment of the magnetic material. A ceramic material consisting of the following components has been found to be satisfactory for this purpose when permalloy is employed as the magnetic material:

Parts by weight The heat treatment of the magnetic core after assembly is a desirable feature since it avoids handling of the core after heat treatment, a procedure which is known to lower the magnetic qualities of thin permalloy laminations.

After the magnetic head assembly has been fired, the unwanted ends of the magnetic core or ribbon i6 are clipped and the pointed end of the entire assembly, including the shield I2, is ground and/or lapped until the desired separation of the pole tips 24 and 28 is obtained. The magnetic head unit may be mounted on its associated equipment by means of the mounting holes 28 in the shield [2.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. The method of making an electromagnetic transducer which comprises winding a magnetic core comprising a lamina of magnetic material around a ceramic wafer two opposite sides of which converge to form a point at one end, said core being wound around the periphery, including said pointed end, or said wafer, disposing a ceramic member on which a coil has been wound adjacent said ceramic Wafer in such manner that said magnetic core threads through said coil, disposing an eddy current shield about the pointed end of said ceramic wafer in such manner as to surround that portion of the core which overlies the converging sides of said wafer, coating the entire assembly comprising said wafer,

said coil, said core and said shield with a ceramic materal, firing said ceramic coated assembly to form a glazed coating, and removing the point of said wafer and that portion of the magnetic core disposed adjacent thereto to form two spaced pole tips.

2. The method of making an electromagnetic transducer which comprises winding a magnetic core comprising a lamina of magnetic material around a ceramic wafer triangularly shaped at one end and notched at two opposite sides, said core being wound around the periphery, including said triangularly shaped end of said wafer, disposing a ceramic member on which a coil has been wound adjacent each of said notched sides in such manner that said magnetic core threads through each of said coils, disposing a nonmagnetic eddy current shield about said triangularly-shaped portion of said water in such manner as to surround that portion of the core which overlies the triangularly shaped portion of said wafer, coating the entire assembly comprising said wafer, said coils, said shield and said magnetic core with a ceramic material, firing said ceramic coated assembly to form a glazed ceramic coating, and removing the point of the triangularly-shaped portion of said wafer and that portion of the magnetic core disposed adjacent thereto to form two spaced pole tips.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,464,029 Ehrman Mar. 8, 1949 2,592,652 Buhrendori Apr. 15. 1952 

